Re-evaluating the EDM Process for Aerospace Components

Aerospace manufacturing is also changing…

The way in which commercial and military aircraft are designed, developed, and produced continues to undergo significant change in response to the need to cut costs and deliver products faster...

...Increasingly, firms bring together teams composed of customers, engineers, and production workers to pool ideas and make decisions concerning the aircraft at every phase of product development...

Source: Bureau of Labor Statistics, U.S. Department of Labor, Career Guide to Industries, 2008-09 Edition, Aerospace Product and Parts Manufacturing, on the Internet at http://www.bls.gov/oco/cg/cgs006.htm (visited July 15, 2008).

The aerospace improvement imperative:

Reduce cost:

Capital cost

Operating cost

Material cost

Floor space requirements

Reduce time to market:

Reduce secondary operations

No harm to quality and consistency

EDM and Aerospace: Current perspective / Breaking Barriers

What we know about EDM:

EDM can remove material that is otherwise difficult to machine.

EDM does not face the same machining challenges of today’s ultra-tough alloys.

Component material only needs to be electrically conductive.

What we also know about EDM:

Material is removed by heat, thus causing the potential for a recast layer on the parent material.

We are breaking barriers:

We have improved the process to significantly reduce and/or eliminate the recast layer.

Process Review: EDM

Events before electrical discharge

The workpiece and tool are placed in the work position so that they do not touch.

A gap remains, filled by the "dielectric".

The workpiece and tool are connected to a power source via a cable.

A switch is inserted in the connection.

When closed, an electrical voltage is set up between the workpiece and tool.

The electrical discharge.

At first no current flows because the dielectric acts as an insulator.

When the gap is decreased to a given distance (very small), an electrical discharge with spark is struck.

During the discharge, the voltage is decreased and the current causes considerable increase in temperature at the spark point.

This causes small quantities of metal to melt and evaporate.

The formation of the surface

When the switch is opened, the molten material is dispersed just like an explosion.

The discharge channel is deionized and a small crater remains.

Summary of the EDM Process:

ELECTRICAL DISCHARGE
MACHINING (EDM)

A controlled spark is struck between conductive materials.

The sparks cause a series of small craters, with consequent material removal.

The EDM improvement imperative:

The 21st century wire EDM generator:

Improved surface integrity

Improved speed

Improved energy efficiency

History of Generator/Servo technology in the 20th century

The early years: wire EDM

History of Generator/Servo technology in the 21st century

Improving Performance

Electronics Efficiency = Spark Efficiency

Innovations:

Process control as close to the spark as possible

High, process-dedicated computer performance (40 MIPS)

Complete digital data aquisition

FPGA technology

Results:

Fast, precise servo

Optimal and fast process control

Constant EDM results

New Generator results:

Material: Inconel

Material: Titanium

Titanium Surface Oxidation: Then and Now

Surface oxidation caused when machining titanium.
On the right side is the old generator; on the left side is the new generator.

Wire EDM erosion speed in the 21st century

Improving Erosion Speed

The 21st century Die-SInk EDMgenerator:

Improved surface integrity

Improved speed

Improved energy efficiency

History of Generator/Servo technology in the 20th century

The early years: Die-sink EDM

History of Generator/Servo technology in the 21st century

The early years: Improving Performance

Wire EDM Spark vs. Die-sink EDM Spark

Improving Performance

Intelligent Pulse Generators

Innovations:

Process control as close to the spark as possible

High, process-dedicated computer performance (40 MIPS)

Complete digital data aquisition

FPGA technology

Results:

Fast, precise servo

Optimal and fast process control

Constant EDM results

Programmed discharge during asymptotic state

Patented process

Results of intelligent spark discharge

Patented process

Waiting for the right moment...

Patented process

Almost...but not yet!

Patented process

We're getting close!

Patented process

Discharge at the “end phase” of the pulse

Patented process

Intelligent spark discharge: why it works

Asymptotic behavior determines that the discharge voltage is in balance with the instantaneously flowing discharge current.

Current amplitude is increased just before the end of the pulse

The high energy at the “end phase” of the pulse prevents re-solidification of the fused phase.